UPSC Prelims 2009 Q103: Science & Technology – Logical Reasoning & Puzzles
- (a) Brother
- (b) Sister
- (c) Father
- (d) Cannot be established (cannot be determined)
Answer: (d) Cannot be established (cannot be determined)
Explanation
A family relationships logic puzzle
Six family members — A, B, C, D, E, F — with specific profession and marriage clues.
| Clue | Deduction |
|---|---|
| D (salesman) married to the lady teacher | One couple: D and the teacher |
| Doctor married to the lawyer | Another couple: doctor and lawyer |
| F (accountant) is B's son and E's brother/sibling | B and spouse are parents of F and E |
| C (lawyer) is A's daughter-in-law | C is married to A's son, who must be B (since F, E are B's children) — so B is the doctor, married to C, the lawyer |
| E is the unmarried engineer | E's gender is never specified in any clue |
| A is F's grandmother | A and D (the remaining couple) are the grandparents, with D as the teacher's husband — so A is the teacher, married to D |
Why E's relationship to F can't be pinned down:
| Point | Detail |
|---|---|
| E is confirmed as F's sibling | Both are children of B (doctor) and C (lawyer) |
| E's gender | Never stated anywhere in the clues — unlike F, who is explicitly called a 'son' |
| Conclusion | Since E's gender is unknown, we cannot determine if E is F's brother or sister |
Answer: (d) Cannot be established (cannot be determined).
Why each option is right or wrong
- (a) Incorrect. We cannot confirm E is male, so 'Brother' cannot be stated with certainty.
- (b) Incorrect. We cannot confirm E is female either, so 'Sister' cannot be stated with certainty.
- (c) Incorrect. E is clearly F's sibling (both children of B and C), not F's father.
- (d) CORRECT. Since E is confirmed as F's sibling but E's gender is never specified, the exact brother/sister relationship cannot be determined.
Key point
E is confirmed as F's sibling (both are children of B, the doctor, and C, the lawyer) — but since E's gender is never stated in any clue, whether E is F's brother or sister cannot be established.
Remember
Family puzzle: E and F are siblings (children of B the doctor and C the lawyer), but E's gender is never specified, so the brother/sister relationship cannot be determined.
Common mistakes
- Assuming E must be male or female based on no actual textual evidence, just the pattern of other characters.
- Missing that F is explicitly called 'son', while E's gender is conspicuously never mentioned.
- Not systematically checking whether a puzzle's clues fully determine every requested relationship before answering.
Exam tip
When a puzzle gives you a sibling relationship but never states one sibling's gender, the specific brother/sister answer cannot be determined — a common 'trap' answer choice.
Sources
- R. S. Aggarwal — A Modern Approach to Verbal and Non-Verbal Reasoning (Blood Relations)
- R. S. Aggarwal — A Modern Approach to Verbal and Non-Verbal Reasoning (Puzzle Test)